As regards the tilt of their orbits, some are actually as much as 34 degrees inclined to the ecliptic, so that in fact they are seen from the Earth among our polar constellations.

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From all this you see that Mars occupies a rather hot comer in the solar system.  Is it not possible that more than once in the remote past Mars may have encountered one of these wanderers?  If he came within a certain distance of the small body his great mass would sway it from its orbit, and under certain conditions he would pick up a satellite in this manner.  That his present satellites were actually so acquired is the suggestion of Newton, of Yale College.

Mars’ satellites are indeed suspiciously and most abnormally small.  I have not time to prove this to you by comparison with the other worlds of the solar system.  In fact, they were not discovered till 1877—­although they were predicted in a most curious manner, with the most uncannily accurate details, by Swift.

One of these bodies is about 36 miles in diameter.  This is Phobos.  Phobos is only 3.700 miles from the surface of Mars.  The other is smaller and further off.  He is named Deimos, and his diameter is only 10 miles.  He is 12,500 miles from Mars’ surface.  With the exception of Phobos the next smallest satellite known in the solar system is one of Saturn’s—­Hyperion; almost 800 miles in diameter.  The inner one goes all round Mars in 71/2 hours.  This is Phobos’ month.  Mars turns on his axis in 24 hours and 40 minutes, so that people in Mars would see the rise of Phobos twice in the course of a day and night; lie would apparently cross the sky

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going against the other satellite; that is, he would move apparently from west to east.

We may at least assume as probable that other satellites have been gathered by Mars in the past from the army of asteroids.

Some of the satellites so picked up would be direct:  that is, would move round the planet in the direction of his axial rotation.  Others, on the chances, would be retrograde:  that is, would move against his axial rotation.  They would describe orbits making the same various angles with the ecliptic as do the asteroids; and we may be sure they would be of the same varying dimensions.

We go on to inquire what would be the consequence to Mars of such captures.

A satellite captured in this manner is very likely to be pulled into the Planet.  This is a probable end of a satellite in any case.  It will probably be the end of our satellite too.  The satellite Phobos is indeed believed to be about to take this very plunge into his planet.  But in the case when the satellite picked up happens to be rotating round the planet in the opposite direction to the axial rotation of the planet, it is pretty certain that its career as a satellite will be a brief one.  The reasons for this I cannot now give.  If, then, Mars picked up satellites he is very sure to have absorbed them sooner or later.  Sooner if they happened to be retrograde satellites, later if direct satellites.  His present satellites are recent additions.  They are direct.